This invention relates to the passivation of dielectric surfaces of semiconductors, and more particularly, this invention relates to a method of treating a hydrogenated silicon-oxy-carbide dielectric surface layer to dehydroxylate the dielectric surface layer.
One area of interest in semiconductor manufacture has been the use of hydrogenated silicon-oxy-carbide glass and the associated methods to form a low dielectric constant inter-metal dielectric constant film.
Much study has already been accomplished with the use of the reactions between silicon, carbon and oxygen, especially for the use of xe2x80x9cnicalonxe2x80x9d fibers and composite ceramics. Some of these products have been used in fiber optic applications. An example is the silicon-oxy-carbide glass method of preparation and associated product disclosed in U.S. Pat. No. 5,180,694 to Renlund et al., the disclosure which is hereby incorporated by reference in its entirety. It has been found that these types of materials can also be used in the semiconductor industry.
These low dielectric constant (low k) inter-metal dielectrics are applicable with silicon-oxy-carbide glass and, reduce parasitic capacitance. Amorphous, hydrogenated silicon-oxy-carbide (xcex1-SiOC:H) has been found to be a viable low k material for advanced integrated circuit technology applications, such as with copper. Chemical vapor deposition (CVD) of xcex1-SiOC:H glass found a mixture of alkyl-silane and nitrous-oxide has a dielectric constant (k) of about 2.5 to 3.0, as compared to conventional SiO2 with a dielectric constant xe2x89xa73.9. The k value of the xcex1-SiOC:H film is directly proportional to the carbon content where a higher carbon content yields a lower k. A higher carbon content creates problems with conventional lithography pattern transfer because of a reduced chemical etch selectivity between the xcex1-SiOC:H and the polymer photo resist material. Another prior art method for reducing the dielectric constant (k) is to make it porous, basically encapsulating voids in the xcex1-SiOC:H film. This results in a suitable low k film, with a carbon content of about 5-20 atomic percent. However, dangling sites cause the film""s dielectric properties to be unstable.
Prior art attempts to correct the unstable dielectric properties have included the excessively long curing in oxygen and/or nitrogen, or capping the porous xcex1-SiOC:H film with a barrier, such as silicon nitride. The long cure (2-5 hours) is expensive in terms of cycle time and additional facility requirements. Furthermore, the films are not completely stable because bond sites are not fully passivated. The barrier films have a higher dielectric constant (typically  greater than  greater than 4.0) which increases the effective k.
There has been some chemical treatment for silica-containing glass-surface using strained siloxane rings, such as disclosed in U.S. Pat. No. 5,965,271 to Grabbe et al., the disclosure which is hereby incorporated by reference in its entirety. However, the 271 disclosure is directed to a more conventional silica-containing glass surface and not the silicon-oxy-carbide semiconductor surface layer as in the present invention.
It is therefore an object of the present invention to passivate a deposited polysilicon-oxy-carbide dielectric surface layer to dehydroxylate the dielectric surface layer without impairing its function.
The present invention cures the xcex1-SiOC:H layer in an alkyl environment, thus effectively changing the Sixe2x80x94OH, SiH and SIxe2x80x94O into Sis (CH3). This passivation cure is performed insitu in a plasma enchanced (PE-) CVD reactor by dissociating methane, acetylene or any other alkyl component, such as hexamethyldisilane (HMDS) or methyltriacetoxysilane (MTAS).
In still another method aspect of the present invention, the dielectric surface layer deposited over a semiconductor substrate is treated in an alkyl environment. The dielectric surface layer comprises a deposited silicon-oxy-carbide layer having a carbon content ranging from about 5% to about 20% at the molecular level and a dielectric constant of about 2.5 to about 3.0. The method comprises the steps of positioning the semiconductor substrate within a chemical vapor deposition chamber and heating the dielectric surface layer. The dielectric surface layer is annealed within an alkyl environment of the chemical vapor deposition chamber to passivate the dielectric surface layer while bonding with the silicon an attaching alkyl terminating chemical species on the dielectric surface layer to aid in dehydroxylating the dielectric surface layer.
The step of heating further comprises the step of heating with a plasma within the chemical vapor deposition chamber. The heating step with a plasma can occur at a power of about 100 to about 500 watts. A radio frequency induced current can be generated and typically is about 12 to about 14 MHz. The annealing can occur within a vacuum environment of about 1 to about 10 Torr.
In still another aspect of the present invention, a semiconductor article includes a semiconductor substrate and deposited polysilicon-oxy-carbide dielectric surface layer having a carbon content ranging from about 5% to about 20% at the molecular level and a passivated surface layer has a terminating chemical species that is substantially free of hydroxyl and formed by heating the silicon-oxy-carbide dielectric surface layer within a chemical vapor deposition chamber and contacting the surface layer with an alkyl to bond molecules via Sixe2x80x94Oxe2x80x94Si chains and dehydroxylate the surface layer. The alkyl group in one aspect of the present invention can be selected from the group consisting of: acetylene, methane, hexamethyldisilane and methyltriacetoxysilane to bond molecules via Sixe2x80x94Oxe2x80x94Si chains and dehydroxylate the surface. The hexarmethyldisilane and the methyltriacctoxysilane are about 1% to about 30% concentration.